Cloud Computing
Computer Science Department
Chapter Three
Cloud Computing Architecture
3.1 Cloud Components
Cloud Components In a simple, topological sense, a cloud computing solution is made
up of several elements: clients, the data center, and distributed servers. As shown in Figure
3-1, these components make up the three parts of a cloud computing solution. Each
element has a purpose and plays a specific role in delivering a functional cloud based
application, so let’s take a closer look.
Figure 3.1 Thee components make up cloud computing solution.
1-Clients
Clients are, in a cloud computing architecture, the exact same things that they are in a
plain, old, everyday local area network (LAN). They are, typically, the computers that just
sit on your desk. But they might also be laptops, tablet computers, mobile phones, or
PDAs—all big drivers for cloud computing because of their mobility. Anyway, clients are
the devices that the end users interact with to manage their information on the cloud.
Clients generally fall into three categories:
Dr. Rafaa Ismael Yahya
Page 13
Cloud Computing

Computer Science Department
Mobile:Mobile devices include PDAs or smartphones, like a Blackberry,
Windows Mobile Smartphone, or an iPhone.

Thin Clients are computers that do not have internal hard drives, but rather
let the server do all the work, but then display the information.

Thick Clients This type of client is a regular computer, using a web browser
like Firefox or Internet Explorer to connect to the cloud.
Thin clients are becoming an increasingly popular solution, because of their price and
effect on the environment. Some benefits to using thin clients include
2-Data Center
The data center is the collection of servers where the application to which you
subscribe is housed. It could be a large room in the basement of your building or a room
full of servers on the other side of the world that you access via the Internet. A growing
trend in the IT world is virtualizing servers. That is, software can be installed allowing
multiple instances of virtual servers to be used. In this way, you can have half a dozen
virtual servers running on one physical server.
3-Distributed Servers
But the servers don’t all have to be housed in the same location. Often, servers are in
geographically disparate locations. But to you, the cloud subscriber, these servers act as if
they’re humming away right next to each other. This gives the service provider more
flexibility in options and security. For instance, Amazon has their cloud solution in servers
all over the world. If something were to happen at one site, causing a failure, the service
would still be accessed through another site. Also, if the cloud needs more hardware, they
need not throw more servers in the safe room—they can add them at another site and
simply make it part of the cloud.
Dr. Rafaa Ismael Yahya
Page 14
Cloud Computing
3.2
Computer Science Department
5-4-3 Principles of Cloud computing
The 5-4-3 principles put forth by NIST describe as shown in Figure 3.2 (a) the five
essential characteristic features that promote cloud computing, (b) the four deployment
models that are used to narrate the cloud computing opportunities for customers while
looking at architectural models, and (c) the three important and basic service offering
models of cloud computing.
Figure 3.2 Architecture of cloud computing
3.3 Five Essential Characteristics
Cloud computing has five essential characteristics, which are shown in Figure 3.3.
Readers can note the word essential, which means that if any of these characteristics is
missing, then it is not cloud computing:
Dr. Rafaa Ismael Yahya
Page 15
Cloud Computing
Computer Science Department
1. On-demand self-service: A consumer can unilaterally provision computing
capabilities, such as server time and network storage, as needed automatically
without requiring human interaction with each service’s provider.
2. Broad network access : Capabilities are available over the network and
accessed through standard mechanisms that promote use by heterogeneous
thin or thick client platforms (e.g., mobile phones, laptops, and personal
digital assistants [PDAs])
Figure 3.3 the essential characteristics of cloud computing
3. Elastic resource pooling: The provider’s computing resources are pooled to
serve multiple consumers using a multi-tenant model, with different physical
and virtual resources dynamically assigned and reassigned according to
consumer demand. There is a sense of location independence in that the
customer generally has no control or knowledge over the exact location of the
provided resources, but may be able to specify the location at a higher level
of abstraction (e.g., country, state, or datacenter). Examples of resources
include storage, processing, memory, and network bandwidth.
4. Rapid elasticity: Capabilities can be rapidly and elastically provisioned, in
some cases automatically, to quickly scale out and rapidly released to quickly
Dr. Rafaa Ismael Yahya
Page 16
Cloud Computing
Computer Science Department
scale in. To the consumer, the capabilities available for provisioning often
appear to be unlimited and can be purchased in any quantity at any time.
5. Measured service: Cloud systems automatically control and optimize
resource use by leveraging a metering capability at some level of abstraction
appropriate to the type of service (e.g., storage, processing, bandwidth, and
active user accounts). Resource usage can be monitored, controlled, and
reported providing transparency for both the provider and consumer of the
utilized service.
3.4 Cloud Computing Models
Cloud computing is a model that enables the end users to access the shared pool of
resources such as compute, network, storage, database, and application as an ondemand service without the need to buy or own it. The services are provided and
managed by the service provider, reducing the management effort from the end user side..
The National Institute of Standards and Technology (NIST) defines three basic service
models, namely, IaaS, PaaS, and SaaS, as shown in Figure 3.4 .The NIST definition of the
three basic service models is given as follows:
Figure 3.4 Basic cloud service models
Dr. Rafaa Ismael Yahya
Page 17
Cloud Computing
Computer Science Department
1- lnfrastructure as a Service (IaaS):
The ability given to the infrastructure architects to deploy or run any software on the
computing resources provided by the service provider. Here, the underlying infrastructures
such as compute, network, and storage are managed by the service provider. Thus, the
infrastructure architects are exempted from maintaining the data center or underlying
infrastructure. The end users are responsible for managing applications that are running on
top of the service provider cloud infrastructure. Generally, the IaaS services are provided
from the service provider cloud data center.
The end users can access the services from their devices through web command line
interface (CLI) or application programming interfaces (APIs)provided by the service
providers. Some of the popular IaaS providers include Amazon Web Services (AWS),
Google Compute Engine,OpenStack, and Eucalyptus.
Benefits of IaaS
allows the cloud provider to freely locate the infrastructure over the Internet in a costeffective manner. Some of the key benefits of IaaS are listed below:
1. Full Control of the computing resources through Administrative Access to
VMs.
2. Flexible and Efficient renting of Computer Hardware.
3. Portability, Interoperability with Legacy Applications.
2- Platform as a Service (PaaS):
The ability given to developers to develop and deploy an application on the
development platform provided by the service provider. Thus, the developers
are exempted from managing the development platform and underlying infrastructure.
Here, the developers are responsible for managing the deployed application and
configuring the development environment. Generally, PaaS services are provided by the
service provider on an on-premise or dedicated or hosted cloud infrastructure.
The developers can access the development platform over the Internet through web
CLI, web user interface (UI), and integrated development environments (IDEs). Some
Dr. Rafaa Ismael Yahya
Page 18
Cloud Computing
Computer Science Department
of the popular PaaS providers include Google App Engine, Force.com, RedHat OpenShift,
Heroku, and Engine Yard.
Benefits of the PaaS model include:
1. Lower administrative overhead: Consumer need not to bother much about
the administration because it's the responsibility of cloud provider.
2. Lower total cost of ownership: Consumer need not purchase expensive
hardware, servers, power and data storage.
3. Scalable solutions: It is very easy to scale up or down utomatically based on
application resource demands.
4. More current system software:It is the responsibility of the cloud provider
to maintain software versions and patch installations
3-Software as a Service (SaaS):
The ability given to the end users to access an application over the Internet that is
hosted and managed by the service provider. Thus, the end users are exempted from
managing or controlling an application, the development platform, and the underlying
infrastructure. Generally, SaaS services are hosted in service provider–managed or service
provider–hosted cloud infrastructure.
The end users can access the services from any thin clients or web browsers. Some of
the popular SaaS providers include Saleforce.com, Google Apps, and Microsoft office
365.
Dr. Rafaa Ismael Yahya
Page 19
Cloud Computing
Computer Science Department
Benefits of the SaaS model include:
1. easier administration
2. automatic updates and patch management
3. compatibility: All users will have the same version of software.
4. easier collaboration, for the same reason
5. global accessibility.
The different cloud service models target different audiences. For example,
IaaS model targets the information technology (IT) architects, PaaS targets the
developers, SaaS targets the end users.
Based on the services subscribed, the responsibility of the targeted audience
may vary as shown in Figure 3.5.
In IaaS, the end users are responsible for maintaining the development
platform and the application running on top of the underlying infrastructure. The IaaS
providers are responsible for maintaining the underlying hardwareas shown in Figure
3.5a.
In PaaS, the end users are responsible for managing the application that they
have developed. The underlying infrastructure will be maintained by the infrastructure
provider as shown in Figure 3.5b.
In SaaS, the end user is free from maintaining the infrastructure, development
platform, and application that they are using. All the maintenance will be carried out
by the SaaS providers as shown Figure 3.5c.
Figure 3.5 User and service provider responsibilities of cloud service models: (a) IaaS, (b) PaaS, and
(c) SaaS.
Dr. Rafaa Ismael Yahya
Page 20
Cloud Computing
Computer Science Department
3.5 Cloud Deployment Models
Deployment models can be defined as the different ways in which the cloud can be
deployed. These models are fully user centric, that is, these depend on users’
requirement and convenience. A user selects a model based on his or her requirement
and needs. The NIST defines four different types of cloud deployment models in the
cloud:
1. Private cloud
2. Public cloud
3. Community cloud
4. Hybrid cloud
The service delivery of cloud services through different deployment models is shown
in Figure 3.6.
Figure 3.6 Deployment and delivery of different cloud service delivery models.
The classification of the cloud is based on several parameters such as the size
of the cloud (number of resources), type of service provider, location, type of users,
security, and other issues. The smallest in size is the private cloud (Figure 3.7).
Dr. Rafaa Ismael Yahya
Page 21
Cloud Computing
Computer Science Department
The private cloud is the most basic deployment model that can be deployed by
a single organization for its personal use. It is not shared by other organizations, and it
is not allowed for public use. The private cloud is to serve the people of an
organization. It is usually on premise but can be outsourced also. The next one is the
community cloud, which is an extension of the private cloud. Here, the cloud is the
same as the private cloud but is shared by several organizations. The community
cloud is established for a common cause.
Figure 3.7 Cloud deployment models.
The cause can be anything, but usually it leads to mutual benefits among the
participating organizations. The next is the public cloud, which is the opposite of the
private cloud. This cloud allows access from any place in the world and is open to the
public. This cloud is biggest in size among all other deployment models. The public cloud
model is one of the most popular deployment models. The public cloud service provider
charges the users on an hourly basis and serve the users according to the service-level
agreements (SLAs), which are discussed in the succeeding sections. The next one is the
hybrid cloud, which is a combination of other deployments. Usually, it consists of the
private and public clouds combined. Several properties of the private cloud are used with
the properties of the public cloud. This cloud is one of the upcoming cloud models
growing in the industry. All four types of cloud deployments are discussed in detail in
subsequent sections.
Dr. Rafaa Ismael Yahya
Page 22
Cloud Computing
Computer Science Department
3.5.1 Private Cloud
In this section, the private cloud deployment model is discussed. According to the
National Institute of Standards and Technology (NIST), private cloud can be defined as the
cloud infrastructure that is provisioned for exclusive use by a single organization
comprising multiple consumers (e.g., business units). It may be owned, managed, and
operated by the organization, a third party, or some combination of them, and it may exist on
or off premises .The private cloud in simple terms is the cloud environment created for a
single organization. It is usually private to the organization but can be managed by the
organization or any other third party. Private cloud can be deployed using Open source tools
such as Open stack, Eucalyptus. The private cloud is small in size as compared to other cloud
models. Here, the cloud is deployed and maintained by the organizations itself.
1.Characteristics
Certain characteristics of the private cloud are as follows:
1. Secure: The private cloud is secure. This is because usually the private cloud is
deployed and managed by the organization itself, and hence there is least chance
of data being leaked out of the cloud. In the case of outsourced cloud, the service
provider may view the cloud (though governed by SLAs), but there is no other
risk from anybody else as all the users belong to the same organization.
2. Central control: The organization mostly has full control over the cloud as
usually the private cloud is managed by the organization itself. Thus, when
managed by the organization itself, there is no need for the organization to rely
on anybody.
Dr. Rafaa Ismael Yahya
Page 23
Cloud Computing
Computer Science Department
3. Weak SLAs: Formal SLAs may or may not exist in a private cloud. But if they
exist they are weak as it is between the organization and the users of the same
organization. Thus, high availability and good service may or may not be
available. This depends on the organization that is controlling the cloud.
2. Suitability
Suitability refers to the instances where this cloud model can be used. It also
signifies the most suitable conditions and environment where this cloud model can be
used, such as the following:
1. The organizations or enterprises that require a separate cloud for
their personal or official use.
2. The organizations or enterprises that have a sufficient amount of
funds as managing and maintaining a cloud is a costly affair
3. The organizations or enterprises that consider data security to be
important
4. The organizations that want autonomy and complete control over
the cloud
5. The organizations that have a less number of users.
6. The organizations that have prebuilt infrastructure for deploying the
cloud and are ready for timely maintenance of the cloud for efficient
functioning.
7. Special care needs to be taken and resources should be available for
troubleshooting.
2. The private cloud platform is not suitable for the following:
• The organizations that have high user base
•
The organizations that have financial constraints
•
The organizations that do not have prebuilt infrastructure
Dr. Rafaa Ismael Yahya
Page 24
Cloud Computing
Computer Science Department
3. Advantages
•
The cloud is small in size and is easy to maintain.
•
It provides a high level of security and privacy to the user.
•
It is controlled by the organization.
4. Disadvantages
•
For the private cloud, budget is a constraint.
•
The private clouds have loose SLAs.
3.5.2 Public Cloud
According to NIST, the public cloud is the cloud infrastructure that is provisioned
for open use by the general public. It may be owned, managed, and operated by a business,
academic, or government organization, or some combination of them. It exists on the
premises of the cloud provider. The typical public cloud is depicted in Figure 3.8. Public
cloud consists of users from all over the world. A user can simply purchase resources on an
hourly basis and work with the resources. There is no need of any prebuilt infrastructure for
using the public cloud. These resources are available in the cloud
provider’s premises.
Usually, cloud providers accept all the requests , and hence, the resources in the service
providers’ end are considered infinite in one aspect. Some of the well-known examples of the
public cloud are Amazon AWS, Microsoft Azure, etc.
Dr. Rafaa Ismael Yahya
Page 25
Cloud Computing
Computer Science Department
1. Characteristics
1. Highly scalable: The public cloud is highly scalable. The resources in the public
cloud are large in number and the service providers make sure that all the
requests are granted. Hence, the public cloud is considered to be scalable.
2. Affordable: The public cloud is offered to the public on a pay-as-you-go basis;
hence, the user has to pay only for what he or she is using (usually on a per-hour
basis). And, this does not involve any cost related to the deployment.
Figure 3.8 public cloud
3. Less secure: The public cloud is less secure out of all the four deployment
models. This is because the public cloud is offered by a third party and they have
full control over the cloud. Though the SLAs ensure privacy, still there is a high
risk of data being leaked.
4. Highly available:
The
public
cloud
is
highly
any body from any part of the world can access the public
available
because
cloud with
proper
permission, and this is not possible in other models as geographical or other
access restrictions might be there.
5. Stringent SLAs: SLA is very stringent in the case of the public cloud. As the
service provider’s business reputation and customer strength are totally dependent
on the cloud services, they follow the SLA strictly and violations are avoided.
These SLAs are very competitive.
Dr. Rafaa Ismael Yahya
Page 26
Cloud Computing
Computer Science Department
2. Suitability
There are several occasions and environments where the public cloud is
suitable. Thus, the suitability of the public cloud is described. The public cloud can
be used whenever the following applies:
1. The requirement for resources is large, that is, there is large user
base.
2. The requirement for resources is varying.
3. There is no physical infrastructure available.
4. An organization has financial constraints.
3. The public cloud is not suitable, where the following applies:
 Security is very important.

Organization expects autonomy.

Third-party reliability is not preferred.
3. Issues
Several issues pertaining to the public cloud are as follows:
1. SLA: Unlike the private cloud, here the number of users is more and so are the
numbers of service agreements. The service provider is answerable to all the
users. The users here are diverse. The SLA will cover all the users from all parts
of the world. The service provider has to guarantee all the users a fair share
without any priority. Having the same SLA for all users is what is usually
expected, but it depends on the service provider to have the same SLA for all the
users irrespective of the place they are.
2. Network: The network plays a major role in the public cloud. Each and every
user getting the services of the cloud gets it through the Internet. The services are
accessed through the Internet by all the users, and hence, the service delivery
wholly depends on the network. Unlike the private cloud where the organization
takes responsibility for the network, here the service provider is not responsible
for the network. The service provider is responsible for providing proper service
to the customer, and once the services are given from the service provider, it goes
Dr. Rafaa Ismael Yahya
Page 27
Cloud Computing
on
Computer Science Department
in
transit
to
the
user.
The
user
will be charged for even if he or she has problem due to the network.The network
usually consists of a high bandwidth and has a low latency. This is because the
connection is only inside the organization. Network management is easier
in this case.
3. Performance: As mentioned, the performance of a cloud delivery model
primarily depends on the network and the resources. The service provider has to
adequately manage the resources and the network. As the number of users
increases, it is a challenging task for the service providers to give good
performance.
4. Multitenancy: The resources are shared, that is, multiple users share the
resources, hence the term multitenant. Due to this property, there is a high risk of
data being leaked or a possible unprivileged access.
5. Location: The location of the public cloud is an issue. As the public cloud is
fragmented and is located in different regions, the access to these clouds involves
a lot of data transfers through the Internet. There are several issues related to the
location. For example, a user from India might be using the public cloud and he
might have to access his personal resources from other countries. This is not good
as the data are being stored in some other country.
6. Security and data privacy : Security and data privacy are the biggest challenges
in the public cloud. As data are stored in different places around the globe, data
security is a very big issue. A user storing the data outside his or her country has
a risk of the data being viewed by other people as that does not come under the
jurisdiction of the user’s country. Though this might not always be true, but it
may happen.
7. Laws and conflicts: The data are stored in different places of the world in
different countries. Hence, data centers are bound to laws of the country in which
they are located. This creates many conflicts and problems for the service
providers and the users.
8. Cloud management: Here, the number of users is more, and so the management
is difficult. The jobs here are time critical, and as the number of users increases, it
becomes more difficult. Inefficient management of resources will lead to resource
shortage, and user service might be affected. It has a direct impact on SLA and
may cause SLA violation.
Dr. Rafaa Ismael Yahya
Page 28
Cloud Computing
Computer Science Department
9. Maintenance: Maintaining the whole cloud is another task. This involves
continuous check of the resources, network, and other such parameters for longlasting efficient delivery of the service. There source provider has to continuously
change the resource components from time to time. The task of maintenance is
very crucial in the public cloud. The good the cloud is maintained, the better is
the quality of service. Here, the cloud data center is where the maintenance
happens; continuously, the disks are replaced from time to time.
The issues discussed earlier will help to understand the public cloud. Before using the
public cloud, one has to choose a cloud service provider. One can choose the public cloud
based on certain parameters like SLA violations, security, and cost of resources. Thus, a
cloud’s quality is determined by the SLA violation it does. The less the SLA violation it
does, the better the cloud is. This is one way of selecting the public cloud; another way is
by cost. If the job for which the resources are used is not time sensitive, then the service
provider who offers the least cost is selected. There following are several advantages and
disadvantages of public clouds.
4. Advantages

There is no need of establishing infrastructure for setting up a cloud.

There is no need for maintaining the cloud.

They are comparatively less costly than other cloud models.

Strict SLAs are followed.

There is no limit for the number of users.

The public cloud is highly scalable.

Security is an issue

Privacy and organizational autonomy are not possible.
5. Disadvantages
Dr. Rafaa Ismael Yahya
Page 29
Cloud Computing
Computer Science Department
3.5.3 Community Cloud
According to NIST, the community cloud is the cloud infrastructure that is
provisioned for exclusive use by a specific community of consumers from
organizations that have shared concerns (e.g., mission, security requirements, policy, and
compliance considerations). It may be owned, managed, and operated by one or more of
the organizations in the community, a third party, or some combination of them, and it
may exist on or off premises. It is a further extension of the private cloud. Here, a private
cloud is shared between several organizations. Either the organizations or a single
organization may collectively maintain the cloud.
The main advantage of the public cloud is that the organizations are able to share the
resources among themselves based on specific concerns. Thus, here the organizations are
able to extract the power of the cloud, which is much bigger than the private cloud, and at
the same time, they are able touse it at a usually less cost. The community is formed based
on
any
commoncause,
but
eventually,
all the
members of
the
community
are benefitted.This model is very suitable for organizations that cannot afford a private
cloud and cannot rely on the public cloud either. Figure 4.5 describes the
community cloud.
Figure 3.9 community cloud
Dr. Rafaa Ismael Yahya
Page 30
Cloud Computing
Computer Science Department
1. Characteristics
1. Collaborative and distributive maintenance: The community cloud is wholly
collaborative, and usually no single party has full control over the whole cloud (in
some cases, it may be controlled by one party). This is usually distributive, and
hence, better cooperation gives better results. Even though it may be outsourced,
collaboration based on purpose always proves to be beneficial.
2. Partially secure: Partially secure refers to the property of the com-munity cloud
where few organizations share the cloud, so there is a possibility that the data can
be leaked from one organization to another, though it is safe from the outside
world.
3. Cost effective: The community cloud is cost effective as the whole cloud is being
shared by several organizations or a community. Usually, not only cost but every
other sharable responsibilities are also shared or divided among the groups.
2. Suitability
This kind of cloud is suitable for organizations that
 Want to establish a private cloud but have financial constraint

Do not want to complete maintenance responsibility of the cloud

Want to establish the cloud in order to collaborate with other clouds

Want to have a collaborative cloud with more security features than
the public cloud
3. This cloud is not suitable for organizations that
 Prefer autonomy and control over the cloud

Does not want to collaborate with other organizations

It allows establishing a low-cost private cloud.

It allows collaborative work on the cloud

It allows sharing of responsibilities among the organization.

It has better security than the public cloud.
4. Advantages
Dr. Rafaa Ismael Yahya
Page 31
Cloud Computing
Computer Science Department
4. Disadvantages

Autonomy of an organization is lost

Security features are not as good as the private cloud

It is not suitable if there is no collaboration.
3 .5 .4 Hybrid Cloud
According to NIST, the hybrid cloud can be defined as the cloud infrastructure
that is a composition of two or more distinct cloud infrastructures (private,
community, or public) that remain unique entities but are bound together by
standardized or proprietary technology that enables data and application portability.
The hybrid cloud usually is a combination of both public and private clouds. This is
aimed at combining the advantages of private and public clouds. The usual method of
using the hybrid cloud is to have a private cloud initially, and then for additional
resources, the public cloud is used. There are several advantages of the hybrid cloud. The
hybrid cloud can be regarded as a private cloud extended to the public cloud.
This
aims
at
utilizing
the
power
of
the
public
cloud by retaining the properties of the private cloud. One of the popular examples forthe
hybrid cloud is Eucalyptus . Eucalyptus was initially designed for the private cloud and is
basically a private cloud, but now it also supports hybrid cloud. Figure 3.10 shows the
hybrid cloud. The hybrid cloud can be further extended into a vast area of federated clouds
that is discussed in subsequent chapters.
Figure 3.10 Hybird cloud
Dr. Rafaa Ismael Yahya
Page 32
Cloud Computing
Computer Science Department
1. Characteristics
1. Scalable : The hybrid cloud is a combination of one or more deployment models.
Usually, the private with public cloud gives hybrid cloud. The main reason of
having a hybrid cloud is to use the property of a public cloud with a private cloud
environment. The public cloud is used whenever needed; hence, as the public
cloud is scalable, the hybrid cloud with the help of its public counter part is also
scalable.
2. Partially secure: The hybrid cloud usually is a combination of public andprivate.
The private cloud is considered to be secured, but as the hybridcloud also uses the
public cloud, there is high risk of security breach. Thus, it cannot be fully termed
as secure but as partially secure.
3. Stringent SLAs: As the hybrid cloud involved a public cloud intervention, the
SLAs are stringent and might as per the public cloud service provider. But
overall, the SLAs are more stringent than the private cloud.
4. Complex cloud management: Cloud management is complex and is a difficult
task in the hybrid cloud as it involves more than one type of deployment models
and also the numbers of users are high.
2 Suitability
The hybrid cloud environment is suitable for

Organizations that want the private cloud environment with the
scalability of the public cloud

Organizations that require more security than the public cloud
3. The hybrid cloud is not suitable for

Organizations that consider security as a prime objective

Organizations that will not be able to handle hybrid cloud
management
Dr. Rafaa Ismael Yahya
Page 33
Cloud Computing
Computer Science Department
3 Issues
The cloud can be analyzed in the following aspects:
1. SLA: SLA is one of the important aspects of the hybrid cloud as both private and
public
are involved.
There
is
a
right
combination
of
SLAs between
the clouds. The private cloud does not have stringent agreements, whereas the
public cloud has certain strict rules to be covered. The SLAs to be covered under
each purview are clearly defined, and it wholly depends on the service provider
(private cloud) to provide efficient services to the customers.
2. Network: The network is usually a private network, and when everthere is a
necessity, the public cloud is used through the Internet. Unlike the public cloud,
here there is a private network also. Thus, a considerable amount of effort is
required to maintain the network. The organization takes the responsibility from
the network.
3. Performance: The hybrid cloud is a special type of cloud in which the private
environment is maintained with access to the public cloud whenever required.
Thus, here again a feel of an infinite resource is restored. The cloud provider
(private cloud) is responsible for providing the cloud.
4. Multitenancy: Multitenancy is an issue in the hybrid cloud as it involves the
public cloud in addition to the private cloud. Thus, this property can be misused
and the breaches will have adverse effects as some parts of the cloud go public.
5. Location: Like a private cloud, the location of these clouds can be on premise or
off premise and they can be outsourced. They will have all the issues related to
the private cloud; in addition to that, issues related to the public cloud will also
come into picture whenever there is intermittent access to the public cloud.
6. Security and privacy: Whenever the user is provided services using the public
cloud, security and privacy become more stringent. As it is the public cloud, the
threat of data being lost is high.
7. Laws and conflicts: Several laws of other countries come under the purview as
the public cloud is involved, and usually these public clouds are situated outside
the country’s boundaries.
8. Cloud management: Here, everything is managed by the private cloud service
provider.
Dr. Rafaa Ismael Yahya
Page 34
Cloud Computing
Computer Science Department
9. Cloud maintenance: Cloud maintenance is of the same complexity as the private
cloud; here, only the resources under the purview of the private cloud need to be
maintained. It involves a high cost of maintenance.
The hybrid cloud is one of the fastest growing deployment models, which is now
being discussed because of its characteristics as discussed earlier. The issues discussed
provide an overview about the difference between the other cloud models and the hybrid
cloud model. There is another part of the cloud called as federated cloud that is described
in the subsequent chapter. There are several advantages and disadvantages of the hybrid
cloud.
4. Advantages

It gives the power of both the private and public clouds.

It is highly scalable.

It provides better security than the public cloud

The security features are not as good as the public cloud.

Managing a hybrid cloud is complex.

It has stringent SLAs.
5. Disadvantages
Dr. Rafaa Ismael Yahya
Page 35